NSStream TCP Keep-alive iOS

Question

我已经编写了以下代码来设置带有服务器的流：

-(void)streamOpenWithIp:(NSString *)ip withPortNumber:(int)portNumber;
{
       CFReadStreamRef readStream;
       CFWriteStreamRef writeStream;
       CFStreamCreatePairWithSocketToHost(kCFAllocatorDefault, (__bridge CFStringRef)ip, portNumber, &readStream, &writeStream);

       if(readStream && writeStream)
       {
            CFReadStreamSetProperty(readStream, kCFStreamPropertyShouldCloseNativeSocket, kCFBooleanTrue);
            CFWriteStreamSetProperty(writeStream, kCFStreamPropertyShouldCloseNativeSocket, kCFBooleanTrue);

            //Setup inpustream
            inputStream = (__bridge NSInputStream *)readStream;
            [inputStream setDelegate:self];
            [inputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
            [inputStream open];

            //Setup outputstream
            outputStream = (__bridge NSOutputStream *)writeStream;
            [outputStream setDelegate:self];
            [outputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
            [outputStream open];
       }
}

我能够连接到服务器并发送和接收数据。但我想检查连接是否还在那里。如果我断开与wifi路由器的电缆连接，我仍然可以在流中发送数据，并且没有发生错误。

您可以通过使用计时器发送一些消息并检查是否收到回执，从而在应用程序级别解决此问题。但您也可以在较低级别上使用TCP Keep-Alive技术来解决此问题。

我如何用NSStream实现这一点？如何设置检查间隔？

我假设您可以通过使用TCP Keep-Alive检查流关闭时获得NSStreamEventErrorOcurred？

我已经看过这篇文章了，但我想不通：Keeping a socket connection alive in iOS

谢谢你的帮忙!

Answer 1

您可以使用以下命令获取本机套接字句柄

CFDataRef socketData = CFReadStreamCopyProperty((__bridge CFReadStreamRef)(inputStream), kCFStreamPropertySocketNativeHandle);
CFSocketNativeHandle socket;
CFDataGetBytes(socketData, CFRangeMake(0, sizeof(CFSocketNativeHandle)), (UInt8 *)&socket);
CFRelease(socketData);

然后设置套接字选项(您需要为此使用#include <sys/socket.h>命令)：

int on = 1;
if (setsockopt(socket, SOL_SOCKET, SO_KEEPALIVE, &on, sizeof(on)) == -1) {
   NSLog(@"setsockopt failed: %s", strerror(errno));
}

您可以将此代码放入kCFStreamEventOpenCompleted事件的事件处理函数中：

- (void)stream:(NSStream *)stream handleEvent:(NSStreamEvent)event {
    switch (event) {
        case kCFStreamEventOpenCompleted:
            if (stream == self.inputStream) {
                CFDataRef socketData = CFReadStreamCopyProperty((__bridge CFReadStreamRef)(stream), kCFStreamPropertySocketNativeHandle);
                CFSocketNativeHandle socket;
                CFDataGetBytes(socketData, CFRangeMake(0, sizeof(CFSocketNativeHandle)), (UInt8 *)&socket);
                CFRelease(socketData);

                int on = 1;
                if (setsockopt(socket, SOL_SOCKET, SO_KEEPALIVE, &on, sizeof(on)) == -1) {
                    NSLog(@"setsockopt failed: %s", strerror(errno));
                }
            }
            break;

        /* ... other cases ... */;
    }
}

Answer 2

对于类似的问题，有一个更完整的答案。

有关该应用程序的示例，该应用程序在10秒后开始发送keepalive，每2秒发送一次keppalive，并在4次keepalives后关闭流，但没有回复，请查看此帖子：Is it possible to activate TCP keepalive on Apple iOS devices

还说明了如何设置连接关闭前的重传超时。